ADE7754 datasheet(26/44 Pages) AD

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REV. PrG 01/03

PRELIMINARY TECHNICAL DATA

ADE7754

– 26 –

Important: As the phase shift applied on the current channel

is not -90º as it should be ideally, the reactive power

calculation done in the ADE7754 cannot be used directly for

the reactive power calculation. Consequently, it is recom-

mended to use the ADE7754 reactive power measurement

only to get the sign of the reactive power. The reactive power

can be processed using the power triangle method.

HPF

LPF

Instantaneous Reactive

Power Signal - p(t)

MULTIPLIER

Reactive Power

Signal - P

-89º

Figure 30 - Reactive Power Signal Processing

TOTAL REACTIVE POWER CALCULATION

The sum of the Reactive powers coming from each phase

gives the Total Reactive Power consumption. Different

combinations of the three phases can be selected in the sum

by setting bits 7-6 of the WATMode register (mnemonic

WATMOD[1:0]). Each term of the formula can be disabled

or enabled by the LWATSEL bits of the WATMode register.

It should be noticed that in this mode, the LWATSEL bits

are also used to select the terms of the LVAENERGY

III.

The accumulation of the Reactive Power in the LAENERGY

Power in the LAENERGY register. Under the same signal

conditions (e.g. Current and voltage channels at full scale),

if the accumulation of the active power with PF = 1 during

1 second is Wh1 and the accumulation of the reactive power

with PF = 0 during the same time is VARh1, then Wh1 =

9.546 x VAR1.

Note: IA

*, I

* and I

* represent the current channels samples

after APGAIN correction, High-Pass Filtering and -89º

phase shift in the case of Reactive Energy accumulation.

Reactive Energy accumulation selection

The ADE7754 accumulates the Total Reactive Power signal

in the LAENERGY register for an integer number of half

cycles, as shown in Figure 29. This mode is selected by

setting to logic one bit5 of the WAVMode register (Add.

0Ch). When this bit is set the accumulation of the Active

Energy over half line cycles in the LAENERGY register is

disabled and is done instead in the LVAENERGY register.

In this mode, the accumulation of the Apparent Energy over

half line cycles in the LVAENERGY is no-longer available

- See Figure 31.

Active Power

Reactive Power

Apparent Power

LVAENERGY

Bit5 WAVMode

LAENERGY

Figure 31 - Selection of Reactive energy accumulation

The features of the Reactive Energy accumulation are the

same as the Line Active Energy accumulation:

Each one of three phases zero-crossing detection can contrib-

ute to the accumulation of the half line cycles. Phase A, B and

C zero crossings are respectively taken into account when

counting the number of half line cycles by setting to logic one

bits 4-6 of the MMODE register. Selecting phases for the

Zero crossing counting has also the effect of enabling the

Zero-crossing detection, Zero-crossing Time-Out and Pe-

riod Measurement for the corresponding phase as described

int he Zero-crossing Detection paragraph.

The number of half line cycles is specified in the LINCYC

ADE7754 can accumulate Active Power for up to 65535

combined half cycles. At the end of an energy calibration

cycle the LINCYC flag in the Interrupt Status register is set.

If the LINCYC mask bit in the Interrupt Mask register is

enabled, the IRQ output will also go active low. Thus the IRQ

line can also be used to signal the end of a calibration.

As explained in the Reactive Power paragraph, the purpose

of the reactive Energy calculation in the ADE7754 is not to

give an accurate measurement of this value but to to provide

the sign of the the reactive energy. The ADE7754 provides

an accurate measurement of the Apparent Energy. As the

active energy is also measured in the ADE7754, a simple

mathematical formula can be used to extract the Reactive

energy. The evaluation of the sign of the Reactive Energy

makes up the calculation of the Reactive Energy.

Reactive

Energy

sign

Power

Apparent Energy

Active E

()×−

nergy

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